TY - JOUR T1 - Closed circuit rebreathing to achieve inert gas wash-in for multiple breath wash-out JF - ERJ Open Research JO - erjor DO - 10.1183/23120541.00042-2015 VL - 2 IS - 1 SP - 00042-2015 AU - Alex R. Horsley AU - Katherine O'Neill AU - Damian G. Downey AU - J. Stuart Elborn AU - Nicholas J. Bell AU - Jaclyn Smith AU - John Owers-Bradley Y1 - 2016/01/01 UR - http://openres.ersjournals.com/content/2/1/00042-2015.abstract N2 - Multiple breath wash-out (MBW) testing requires prior wash-in of inert tracer gas. Wash-in efficiency can be enhanced by a rebreathing tracer in a closed circuit. Previous attempts to deploy this did not account for the impact of CO2 accumulation on patients and were unsuccessful. We hypothesised that an effective rebreathe wash-in could be delivered and it would not alter wash-out parameters.Computer modelling was used to assess the impact of the rebreathe method on wash-in efficiency. Clinical testing of open and closed circuit wash-in–wash-out was performed in healthy controls and adult patients with cystic fibrosis (CF) using a circuit with an effective CO2 scrubber and a refined wash-in protocol.Wash-in efficiency was enhanced by rebreathing. There was no difference in mean lung clearance index between the two wash-in methods for controls (6.5 versus 6.4; p=0.2, n=12) or patients with CF (10.9 versus 10.8; p=0.2, n=19). Test time was reduced by rebreathe wash-in (156 versus 230 s for CF patients, p<0.001) and both methods were well tolerated. End wash-in CO2 was maintained below 2% in most cases.Rebreathe–wash-in is a promising development that, when correctly deployed, reduces wash-in time and facilitates portable MBW testing. For mild CF, wash-out outcomes are equivalent to an open circuit.Refinements to wash-in methods permit a faster test and allow use of portable lung clearance index testing http://ow.ly/UYHiN ER -